Casting repair apparatus and method

ABSTRACT

A method and apparatus for repairing a casting in a cold metal repair process includes a plurality of drilling fixtures which facilitate the creation of one or more lock receiving recesses positioned generally transverse to the casting crack. The lock receiving recesses are formed of a single sized circular bore combination having alternating double and single circular portions to maximize strength. A plurality of correspondingly configured metal locks are inserted into the lock receiving recesses to provide transverse metal locks drawing the casting portions on each side of the crack together. A plurality of threaded bores are formed along the remainder of the casting crack in overlapping spacing which receive a corresponding plurality of stitching pins. The stitching pins each define threaded shaft portions having pointed ends and undersized major pitch diameter threads adjacent the pointed ends. A frusto-conical shoulder is formed on the opposite end of the threaded shaft and a break off drive head is coupled to the frustro-conical shoulder by a break off groove structure. When the stitching pins are inserted into their respective threaded bores, the undersized major pitch thread portions facilitate the threading the pin into the threaded bores. The pointed ends of the stitching pins provide complete filling of the threaded bores while the frustro-conical shoulder portions are operative to crush the first few threads of the threaded bores to enhance the seal obtained.

FIELD OF THE INVENTION

[0001] This invention relates generally to casting repair andparticularly to an apparatus and method for cold metal repair forcasting breaks, cracks and other damage.

BACKGROUND OF THE INVENTION

[0002] A great number of machines in use today rely upon cast iron partsor “castings” for strength and reliability. Cast iron is frequentlyselected as the preferred means of fabricating high strength machinecomponents in a virtually endless variety of machine environments. Suchcast iron fabrications include engine blocks, pump housings, manifolds,valve bodies and the like. In large industrial or commercial-typemachines, the castings used in many applications are correspondinglylarge and costly. With all of the advantages which cast iron provides tothe machine fabricator and designer, iron castings are subject toseveral limitations. Perhaps the most significant limitation in theattractiveness of cast iron fabrications in many large machineenvironments arises from the difficulty of repairing such castings inthe event they become cracked, broken or otherwise damaged. In smallmachines, the castings used are correspondingly small and casting repaircapability does not present a significant limitation. This is becausesmall machines may usually be disassembled to completely replace a smallbroken casting. In some environments, even relatively modest sizedmachines are placed in operational environments or physicallyconstricted areas which make disassembly of the machine for castingreplacement impractical. In large machines, the size and cost ofcastings makes their replacement costly and difficult. In certainenvironments in which large machines are used, such as undergroundsystems, the replacement of a damaged casting may be virtuallyimpossible.

[0003] The difficulties and high costs associated with castingreplacement in operating environments such as those described abovecreate a need in the art for apparatus and methods which permit repairrather than replacement of damaged iron castings. However, a significantdisadvantage associated with cast iron fabrications is the difficulty ofrepairing them once they are cracked or otherwise damaged. The metalstructure of most cast metals does not tolerate the use of conventionalmetal repair techniques such as welding or brazing due to the heatassociated with such repair processes. In essence, the application ofheat which accompanies welding or brazing repairs alters the metalstructure of the casting and creates discontinuities of the surroundingmetal. These variations and discontinuities weaken the overall castingstrength in the region of the repair and are, as a result, undesirableand unsatisfactory. Other systems have been tried utilizing adhesivebonding materials such as epoxys or the like. Such systems may besatisfactory for extremely limited applications but have not enjoyedgeneral success in meeting the needs of casting repair.

[0004] In efforts to meet the need for casting repair apparatus andmethods which avoid the damaging effects of heat associated withconventional welding or brazing-type processes, practitioners in the arthave developed certain “cold metal” repair techniques which do notutilize significant heat in affecting casting repair.

[0005] U.S. Pat. No. 4,662,806 issued to Reed sets forth a Metal LockSystem and Method for repairing a casting having a crack therein. Themetal lock is formed of an elongated rigid member having a plurality oflobes formed from adjacent portions thereof in a generally circularcross-section. A pattern of holes is drilled into the casting,transverse to the crack and one or more elongated metal locks are forcedinto the transverse drilled pattern to provide a metal locking actionintended to prevent the cracked portions from spreading apart. Aplurality of threaded holes are then drilled along the crack in anoverlapping pattern and a plurality of threaded fasteners or lacingplugs are threaded into the overlapping holes to complete the castingrepair. The lacing plugs are provided with a driving head and abreak-off groove formed in the fastener. The break-off groove isintended to shear and cause the head portion of the lacing plug to bebroken from the threaded remainder once the lacing plug has beenthreaded into the casting. As a final step, the access of the lacingplugs extending above the surrounding casting surface may be groundaway.

[0006] U.S. Pat. No. 4,845,828 issued to Reed sets forth a Method forRepairing a Metal Casting having a Crack or Break Therein which utilizesapparatus of the type set forth in U.S. Pat. No. 4,662,806. The methodcomprises the drilling of one or more hole patterns transverse to thecasting crack which are characterized by alternate large and smalldiameter holes. One or more correspondingly configured metal locks areembedded into the drilled hole pattern transverse to the casting crack.A plurality of tapered holes are then drilled and tapped along thecasting crack in an overlapping arrangement. The drilling process isfacilitated by the use of a plurality of drilling fixtures or jigs. Aplurality of lacing plugs are threaded into the drilled and tappedapertures. The lacing plugs are configured to include a break awaygroove which causes the head portion of the lacing plug to shear andseparate along the break away groove once the lacing plug is fullyseated. After all metal locks and lacing plugs have been installed, theexcess plug material may be removed by grinding or other processes.

[0007] While the foregoing described prior art apparatus and methods forcold metal repair of damaged castings have enjoyed some success, theenvironment of casting repair remains extremely demanding and repairsremain difficult. Thus, there remains a continuing need in the art forevermore improved apparatus and methods for casting repair. Inparticular, there remains a need for repair systems which function tomore effectively draw the casting portions on each side of a crack ordamaged area together to better prevent spreading of the crack andmisalignment of the crack. Prior art locks have not successfullyachieved this function and often actually tend to spread the castingportions adjacent the crack when the locks are installed. Furthermore,the prior art stitching pins or lacing plugs have, in many instances,failed to form a liquid-tight/gas-tight fit when installed within theirthreaded bores. In addition, the entire casting repair strength is, inmany respects, limited to the strength of the transversely placed metallocks themselves together with the strength of the metal lock grip uponthe casting portions which receive the metal lock. In prior art locks,the design of the metal locks has generally required that the lockstrength be compromised to maintain grip tenacity and thus limit theoverall strength of the casting repair.

[0008] Thus, there remains a continuing need in the art for an improvedapparatus and method for casting repair which overcomes theselimitations of the prior art systems.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is a general object of the present invention toprovide an improved apparatus and method for cold metal casting repair.It is a more particular object of the invention to provide an improvedapparatus and method for cold metal casting repair which more securelyrepairs the casting damage and which draws the repaired casting portionstogether to provide a secure repair and prevent spreading of the crackand realignment of the cracked portion.

[0010] In accordance with the present invention, there is provided foruse in repairing a cracked casting having a crack formed therein, acasting repair apparatus which comprises: at least one metal lockdefining a major axis and defining a center pair of circular lobesspaced apart on each side of the major axis, a plurality of circularlobe pairs equally spaced from the center pair, and a plurality ofsingle circular lobes each centered upon the major axis and interleavedbetween the circular lobe pairs in an overlapping arrangement, thecenter pair of circular lobes, the plurality of circular lobe pairs andthe single circular lobes all having substantially equal radii ofcurvature; a plurality of stitching pins; and means for forming at leastone metal lock recess having a shape corresponding generally to themetal lock.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features of the present invention, which are believed to benovel, are set forth with particularity in the appended claims. Theinvention, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconjunction with the accompanying drawings, in the several figures ofwhich like reference numerals identify like elements and in which:

[0012]FIG. 1 sets forth a perspective view of a metal lock constructedin accordance with the present invention;

[0013]FIG. 1A sets forth a section view of the metal lock of FIG. 1taken along section lines 1A-1A in FIG. 1;

[0014]FIG. 1B sets forth a partial view of the metal lock of FIG. 1;

[0015]FIG. 2 sets forth a side view of a stitching pin constructed inaccordance with the present invention;

[0016]FIG. 2A sets forth a partial section view of the present inventionstitching pin seated within a stitching bore;

[0017]FIG. 3 sets forth a perspective view of the initial drillingoperation of the present invention casting repair method;

[0018]FIG. 4 sets forth a perspective view of the next drilling step inthe present invention method;

[0019]FIG. 5 sets forth a perspective view showing the location of thesecond drilling fixture prior to its locating insertion into the holesprovided in steps 2 and 3;

[0020]FIG. 6 sets forth a perspective view of the casting repair methodfollowing the completion of the drilling of the center row of apertures;

[0021]FIG. 7 sets forth a perspective view of the present inventioncasting repair method following completion of the hole drilling shown inFIG. 6 and the reversal of the drilling fixture;

[0022]FIG. 8 sets forth a perspective view of the present inventioncasting repair following completion of the drilling steps using thefixture of FIGS. 5, 6 and 7 and showing the alignment of the thirddrilling fixture of the invention;

[0023]FIG. 9 sets forth a perspective view of the use of the drillingfixture of FIG. 8 reversed to complete the redrilling of the center rowof apertures;

[0024]FIG. 10 sets forth a perspective assembly view of the insertion ofa plurality of metal locks into the completed drilled metal lock bores;

[0025]FIG. 11 sets forth a perspective view of the present inventioncasting repair method following insertion of the metal locks shown inFIG. 10 and the drilling of the initial threaded bores for the stitchingpins;

[0026]FIG. 12 sets forth a perspective view of the present inventioncasting repair method showing the insertion of stitching pins;

[0027]FIG. 13 sets forth a perspective view of the present inventioncasting repair showing the insertion of the interleaved or overlappingstitching pins; and

[0028]FIG. 14 sets forth a top view of a completed casting repair.

DESCRIPTION OF PREFERRED EMBODIMENT

[0029]FIG. 1 sets forth a perspective view of a metal lock constructedin accordance with the present invention and generally referenced bynumeral 10. Metal lock 10 defines an elongated generally planar memberhaving formed therein a plurality of circular or arced lobes arranged ina predetermined pattern. Specifically, metal lock 10 defines a pair ofoppositely facing circular lobes 11 and 12 having a pair of circularportions 31 and 32 formed on either side thereof. Metal lock 10 furtherdefines a pair of circularly shaped oppositely facing lobes 13 and 14joined to circular portion 32 on one side and to a circular portion 33on the remaining side. A pair of oppositely facing circular lobes 15 and16 are joined to circular portion 33 and form the end lobe pair formetal lock 10. Similarly, a pair of circularly shaped oppositely facinglobes 17 and 18 are joined to circular portion 31 and to a circularportion 30. A pair of oppositely facing circular lobes 19 and 20 arejoined to circular portion 30 and form an end lobe pair for metal lock10. In its preferred form, metal lock 10 is formed of a single generallyplanar high strength metal sheet within which the lobes shown in FIG. 1are formed.

[0030] Metal lock 10 further defines a plurality of upwardly extendingraised projections 50 through 53 and 40 through 44. Projections 50through 53 are generally circular in configuration and are generallycentered upon the upper surface of circular portions 30 through 33respectively. In contrast, projections 40 through 44 are elongated oroval in shape and are generally centered between pairs of oppositelyfacing circular lobes. Specifically, upwardly facing projection 40 isgenerally centered between circular lobes 11 and 12. Similarly,projection 41 is generally centered between circular lobes 13 and 14while projection 42 is generally centered between circular lobes 15 and16. Finally, projection 43 is generally centered between circular lobes17 and 18 while projection 44 is generally centered between circularlobes 19 and 20.

[0031] In accordance with an important aspect of the present invention,it will be apparent to those skilled in the art from examination of FIG.1 that circular portions 30 through 33 as well as circular lobes 11through 20 comprise circular segments having the same size radius. Thus,in essence, the configuration of metal lock 10 is formed by oppositelyfacing circular lobe pairs and interleaved or connecting single circularsegments. In accordance with an important advantage of the presentinvention, the use of circular lobes and circular portions having acommon radius of curvature permits the pattern of drilled bores withinthe to-be-repaired casting to be formed using a single sized finishdrill. In addition, the configuration of metal lock 10 havingalternating lobe pairs provides a maximum strength for metal lock 10together with a secure and tenacious grip thereby upon the castingmaterial in the manner described below.

[0032] In its preferred form, metal lock 10 is fabricated with a subtlevariation of the shape of circular lobes 11 and 12 at the center of themetal lock. Thus, with temporary reference to FIG. 1B, this preferredform of circular lobes 11 and 12 may be shown in greater detail.

[0033]FIG. 1B sets forth an enlarged view of the center portion of metallock 10. For purposes of clarity, projections 40, 51 and 52 are omittedfrom FIG. 1B. As described above, circular lobes 31 and 32 (as well asthe remaining lobes) are symmetrical about center transverse axis 68which bisects lobes 11 and 12 and which is perpendicular to major axis55.

[0034] To provide a closing force when metal lock 10 (and other similarlocks) are inserted into a recess (seen in FIG. 10), lobes 11 and 12 areactually not true circular lobes but rather are formed by offset radii.Specifically, lobe 11 is formed by radii 47 and 49 which are equal tothe radii of the remaining lobes but are symmetrically spaced onopposite sides of center transverse axis 68 at centers 46 and 48respectively. Thus, arcuate portions 57 and 58 which form lobe 11 form aslight point or discontinuity 59 at their junction. Similarly, lobe 12is formed of arcuate portions 76 and 77 having a slight point 78 attheir junction.

[0035] The importance of this structure will be better understoodfollowing the description of the receiving recess for metal lock 10described below. However, suffice it to note here that metal lock 10 is“shorter” than the recess which receives it by a distance referenced bynumeral 56. As a result, metal lock 10 is stretched slightly by thelonger hole pattern of the recess and produces a drawing force tendingto maintain the casting crack in tight closure, but most significantly,to prevent any spreading of the crack. The function of projections 30through 33 and 40 through 44 is set forth below in greater detail.However, suffice it to note here that these projections provide anexpansion mechanism which permits the dimensions of the circular lobesof metal lock 10 to be expanded within the casting recess by simplystriking each of the projections with a suitable shaped punch (in themanner shown in FIG. 1A).

[0036] It will be apparent to those skilled in the art that the presentinvention metal lock may be fabricated in different sizes and havingdifferent lengths while maintaining the proportionate shapes set forthin FIG. 1. It will be equally apparent to those skilled in the art thatmetal lock 10 may, in certain applications, be fabricated without raisedprojections 50 through 53 and 40 through 44 without departing from thespirit and scope of the present invention. In addition, it will also beapparent to those skilled in the art that metal lock 10 may befabricated in a variety of material thicknesses to suit particular needsand applications of the present invention casting repair.

[0037]FIG. 1A sets forth a section view of metal lock 10 taken alongsection lines 1A-1A in FIG. 1. Thus, as set forth above, metal lock 10includes a plurality of circular portions such as circular portion 30together with a plurality of interleaved oppositely facing pairs ofcircular lobes such as circular lobes 17 and 18. Circular portion 30defines an upwardly extending projection 50 which, in its preferredform, is formed by stamping corresponding recess 55 in the underside ofcircular portion 30. Similarly, and with temporary reference to FIG. 1,circular lobes 17 and 18 define a generally centered raised projection43. While not visible in FIG. 1A, it should be apparent that projection43, in its preferred form, is formed within metal lock 10 by stamping acorresponding recess into the underlying portion of metal lock 10.

[0038] In accordance with an important aspect of the present invention,metal lock 10 is expanded when placed within its precision drilledrecess within the casting by applying a suitably shaped punch 35 asshown in dashed line representation in FIG. 1A. With punch 35 positionedas shown, an impact force applied to punch 35 tends to depress theunderlying projection such as projection 50 of metal lock 10 and flattenboth projection 50 and the underlying recess 55. The resultingdisplacement of material caused by the flattening of projection 50 andrecess 55 expands circular portion 30 outwardly in the directionindicated by arrows 36 and 37 causing a tighter fit between metal lock10 and casting recess thereby enhancing the gripping action, seal andstrength of bond for metal lock 10.

[0039]FIG. 2 sets forth a stitching pin constructed in accordance withthe present invention and generally referenced by numeral 60. Stitchingpin 60 defines an elongated threaded shaft 61 supporting a plurality ofexternal threads 62. Shaft 61 terminates at its lower end in a generallycone-shaped pointed end 73. In its preferred form, pointed end 73 has aconical contour which corresponds to the conical angle of the drill usedin the casting repair method set forth below. In accordance with animportant aspect of the present invention, several threads proximate topointed end 73 and referenced by numerals 70, 71 and 72 defineundersized major diameters which facilitates the starting of threads 62within the threaded bores set forth below. Stitching pin 60 furtherincludes a shoulder 63 extending upwardly from the topmost of threads 62of threaded shaft 61. In further accordance with an important aspect ofthe present invention, shoulder 63 is frustro-conical defining a taperedsurface 64. It should be noted that surface 64 of shoulder 63 has agreatest diameter upper portion which extends beyond the greatestdiameter of threads 61 and meets threads 62 of threaded shaft 61 at aleast diameter lower portion with a diameter equal to the externalthread midpoint between the major diameter and minor diameter. A shankportion 66 having a generally cylindrical shape is joined to shoulder 63at a reduced diameter break-off groove 65. The latter is utilized toprovide the shearing of shank 66 from shoulder 63 and separationtherebetween during casting repair described below. Stitching pin 60further includes a hexagonal head 67 joined to shank 66. Head 67 may beshaped in a variety of suitable shapes to accommodate various drivingtools. In the embodiment shown in FIG. 2, head 67 defines a hexagonalshape corresponding to conventional hex head socket driving tools.

[0040] It should be noted that stitching pin 60 avoids the use of atapered shank and this provides full threads over most of its length.The use of undersized major diameters on the first several threads 70,71 and 72 facilitates thread starting without the prior art taperedstructure and its resulting loss of thread and thread bit strength.

[0041] As set forth below in greater detail, a plurality of stitchingpins corresponding to stitching pin 60 are utilized in the presentinvention casting repair. Stitching pin 60 provides substantialimprovement over the stitching pins of the prior art in its provision ofpointed end 73 which cooperates with the drilled receiving bore withinthe casting to more completely fill the bottom portion of the receivingbore. Undersized threads 70 through 72 facilitate the initial threadingof stitching pin 60 into the threaded receiving bore. In furtheraccordance with an important aspect of the present invention, threads 62are preferably formed slightly larger than the corresponding threads inthe tapped threaded bore to provide a tight interference fit andeffective seal between stitching pin 60 and the casting being repaired.In accordance with a still further important aspect of the presentinvention, tapered surface 64 of shoulder 63 is forced against anddriven into the topmost threads of the threaded bore within the castingwhen stitching pin 60 is installed.

[0042]FIG. 2A sets forth a partial section view showing the crushingaction of shoulder 63 of stitching pin 60 as the latter is installedwithin a typical threaded bore. Thus, a portion of a casting 80 definesa threaded bore 81 having internal threads 82 and 83 (shown in dashedline representation) adjacent the upper surface of casting 80. Astitching pin 60, constructed in accordance with the present inventionand shown in FIG. 2, is threaded into threaded bore 81 of casting 80such that threaded shaft 61 is received within threaded bore 81. As canbe seen in FIG. 2A, the outward taper of surface 64 of shoulder 63 isforced against upper threads 82 and 83 of casting 80 with sufficientforce to crush threads 82 and 83 against shoulder 63 thereby displacingthe metal within threads 82 and 83 and forming an extremely tight secureseal between surface 64 of shoulder 63 and casting 80. It should also berecalled that threads 62 of threaded shaft 61 are slightly oversizedbeyond the size of threaded bore 81. This oversizing of threads 62further enhances the seal produced between stitching pin 60 and casting80.

[0043]FIG. 3 sets forth the initial step in the present inventioncasting repair method. A drill fixture 90 having a generally rectangularbody 91 preferably formed of a machine steel or similar material definesa center guide 95, a pin bore 93 (FIG. 4) and a guide bore 92. Pin bore93 (FIG. 4) and guide bore 92 are equally spaced on either side ofcenter guide 95 and have generally equal diameters. A cylindricallocating pin 94 is precisely fitted within pin bore 93 and extends frombody 91 of drill fixture 90. In the position shown in FIG. 3, drillfixture 90 is positioned upon a casting 80 having a to-be-repaired crack84 defined therein. Drill fixture 90 is positioned such that centerguide 95 generally coincides with crack 84. With drill fixture 90 thuspositioned, a conventional drill 85 is lowered in the direction of arrow86 and guided by guide bore 92 to drill a pilot bore having apredetermined depth into casting 80.

[0044]FIG. 4 sets forth the repositioning of drill fixture 90 followingthe successful drill of the initial pilot bore in FIG. 3. Thus, FIG. 4shows drill fixture 90 having a rectangular body 91 defining a guidebore 92 and a downwardly extending locating pin 94. In the position ofFIG. 4, drill fixture 90 has been reversed from its position in FIG. 3causing locating pin 94 to extend downwardly. With drill fixture 90 sooriented, it is lowered toward casting 80 to position locating pin 94within pilot bore 97. Once drill fixture 90 is so positioned, a seconddrilling operation is carried forward in which drill 85 (seen in FIG. 3)is guided again through guide bore 92 to drill a second pilot bore 98(seen in FIG. 5) on the opposite side of crack 84 of casting 80.

[0045]FIG. 5 sets forth a perspective view showing the position of thenext drill fixture generally referenced by numeral 100. As mentioned andshown in FIG. 3 and 4, at this point in the present invention method, apair of pilot bores 97 and 98 have been drilled into casting 80 oneither side of crack 84. Correspondingly, drill fixture 100 includes arectangular body 101 preferably formed of a machine steel materialwithin which a pair of locating pins 102 and 103 are supported indownward extension. The spacing between locating pins 102 and 103corresponds precisely to the spacing provided between pilot bores 97 and98 due to the precise relationship between drill fixtures 100 and 90.Body 101 further defines a pair of equally spaced guide bores 104 and105 between locating pins 102 and 103. In addition, body 101 defines aplurality of larger diameter guide bores 106 through 110 equally spacedin an interleaved arrangement with locating pins 102 and 103 and guidebores 104 and 105.

[0046] Thus, in the position shown in FIG. 5, the next step of thepresent invention casting repair method is carried forward by loweringdrill fixture 100 downwardly to insert locating pins 102 and 103 withinpilot bores 97 and 98 and thus position drill fixture 100 upon thesurface of casting 80. Thereafter, a pair of pilot bores 111 and 112 aredrilled through guide bores 104 and 105 respectively to produce theconfiguration shown in FIG. 6.

[0047]FIG. 6 shows the position of drill fixture 100 following thedrilling of pilot bores 111 and 112. Thereafter, with fixture 100 placedupon casting 80 such that locating pins 102 and 103 are received withinpilot 97 and 98 respectively, a further drilling operation is carriedforward in which larger diameter drills corresponding to the diametersof guide bores 106 through 110 are used to produce a correspondingplurality of equally spaced precisely arranged bores 120 through 124(seen in FIG. 7).

[0048]FIG. 7 sets forth a perspective view of the next step in thepresent invention method of casting repair. Drill fixture 100 is shownraised from casting 80 following the above-mentioned drilling of bores120 through 124 in precise relationship to pilot bores 97, 98, 111 and112. In accordance with an important aspect of the present invention,FIG. 7 shows drill fixture 100 rotated in the direction indicated byarrows 125 through one hundred and eighty degrees rotation to positionguide bores 106 through 110 on the opposite side of pilot bores 97, 98,111, 112. Thus, as drill fixture 100 is again lowered to casting 80 inthe rotated position shown in FIG. 7, locating pins 102 and 103 arereceived in pilot bores 98 and 97 respectively. When so positioned,guide bores 106 through 110 are placed symmetrically opposite bores 120through 124 formed within casting 80 in the previous drilling operation.Thereafter, another drill step takes place in which bores 130 through134 are drilled into casting 80 using guide bores 106 through 110respectively in drill fixture 100. The resulting pattern of bores 130through 134 is better seen in FIG. 8.

[0049] In FIG. 8, the process has reached the point where two preciselypositioned rows of full-sized bores 120 through 124 and 130 through 134are properly formed within casting 80. Also, a plurality of smallerdiameter pilot bores 97, 98, 111 and 112 are precisely positionedbetween the rows of larger diameter bores. At this point, the remainingstep in the present invention process for properly forming the precisionrecess within casting 80 which corresponds to metal lock 10 (seen inFIG. 1) requires merely that pilot bores 97, 98, 111, and 112 beenlarged to the full-size diameter of bores 120 through 124 and 130through 134. Accordingly, an additional drill fixture 140 is now used inplace of drill fixture 100. Drill fixture 140 includes a generallyrectangular body 141 preferably formed of a tool steel or similarmaterial. Drill fixture 140 includes a pair of equally spaced largediameter locating pins 142 and 143 extending upwardly from one side ofbody 141 and a pair of reduced diameter locating pins 144 and 145extending downwardly from the opposite side of body 141. In accordancewith an important requirement for precision drilling of the remainingbores, locating pins 144 and 145 are coaxial with and precisely alignedwith locating pins 142 and 143. In addition, the spacing betweenlocating pins 144 and 145 is precisely equal to twice the spacingbetween adjacent pairs of pilot bores 98 and 111, 97 and 112. Body 141of drill fixture 140 further defines a pair of large diameter guidebores 146 and 147. The spacing between guide bores 146 and 147corresponds precisely to the spacing between adjacent pairs of pilotbores 98 and 111, 97 and 112.

[0050] Thus, with drill fixture 140 positioned in the manner shown inFIG. 8, fixture 140 is lowered to casting 80 such that locating pins 144and 145 are received within pilot bores 111 and 97 respectively. When sopositioned, the next drilling operation is carried forward and pilotbores 98 and 112 are enlarged to the size of guide bores 146 and 147which corresponds to bores 120 through 124 and 130 through 134.Thereafter, pilot bores 111 and 112 may now be enlarged in the nextdrilling operation shown in FIG. 9.

[0051]FIG. 9 sets forth drill fixture 140 in preparation for enlargingpilot bores 97 and 111. Following the drill operation in which bores 98and 112 have been enlarged to provide the bore pattern shown in FIG. 9,drill fixture 140 is rotated one hundred and eighty degrees and invertedwith respect to the position shown in FIG. 8. Thus, as is seen in FIG.9, drill fixture 100 is positioned such that small diameter locatingpins 144 and 145 extend upwardly. In addition, the enlargement of pilotbores 98 and 112 carried forward in the previous drill operation permitsthe precision insertion of locating pins 142 and 143 into the nowenlarged 112 and 98 respectively. With drill fixture 140 positioned uponcasting 80 such that locating pins 142 and 143 are received withinenlarged bores 112 and 98, larger diameter guide bores 146 and 147 areprecisely aligned with pilot bores 97 and 111. Thus, the next drillingstep may be carried forward using guide bores 146 and 147 to enlargepilot bores 97 and 111.

[0052] Once pilot bores 97 and 111 have been enlarged, the lockreceiving recess of the present invention is completely formed and isshown in FIG. 10 and is generally referenced by numeral 150. It will beapparent to those skilled in the art that the depth to which lockreceiving recess 150 is bored is, to some extent, a matter of designchoice to optimize repairs in different castings configurations.However, it has been found advantageous in most casting repairsituations to bore lock receiving recess 150 to a depth approximatelyequal to eighty percent of the casting thickness.

[0053]FIG. 10 sets forth a perspective view of a completed lockreceiving recess properly positioned on each side and traversing acasting crack 84. Also shown in FIG. 10 are a plurality of metal locks160 through 164 shown above and in alignment with lock receiving recess150. In accordance with an important aspect of the present invention, aplurality of relatively thin metal locks configured in accordance withthe structure set forth in FIG. 1 for metal lock 10 are inserted intolock receiving recess 150. This represents a substantial improvementover the prior art structures which attempted to use relatively thickrigid metal locks. Thus, in accordance with the present invention, metallocks 160 through 164 are inserted into lock receiving recess 150. Itshould be noted that while in certain specialized repair situations itmay be desirable to insert metal locks 160 through 164 into recess 150in a single step, it has been found advantageous in most repairsituations to insert each metal lock individually into recess 150. Thisindividual lock insertion permits each lock to be expanded in place bydepressing the raised expansion projections on each metal lock using ahammer and punch in the manner set forth above in FIGS. 1 and 1A. Thus,in accordance with the invention, metal locks 160 through 164 areindividually inserted into lock receiving recess 150 and secured thereinby flattening their respective expansion projections until lockreceiving recess 150 is completely filled and metal locks 160 through174 are tightly situated within recess 150.

[0054] It should be noted that recess 150 is formed without theabove-described “shortening” of the center portion by which lobes 11 and12 of metal lock 10 are formed. Thus, the lobe spacing of the receivingportions of recess 150 is “longer” than the lobe spacing of the metallocks. As a result, the forced insertion of locks 160 through 164 intorecess 150 stretches the metal locks and establishes a drawing forcewhich is exerted upon the casting to maintain closure of the castingcrack and the alignment of casting portions.

[0055]FIG. 11 sets forth the next step in the completion of the presentinvention casting repair method. This step provides for the drilling andtapping of a plurality of stitching pin bores 170 through 177 in agenerally equally spaced arrangement centered along casting crack 84. Itwill be apparent to those skilled in the art that while FIG. 11 setsforth a single lock receiving recess 150 within which a plurality ofmetal locks 160 through 164 (seen in FIG. 10) are received, in mostcasting repair operations a plurality of lock receiving recesses such asrecess 150 are spaced as needed along the length of crack 84 and acorresponding plurality of metal locks are inserted therein. However, itis believed sufficient for purposes of illustration in FIGS. 11 through14 to set forth the present invention method of casting repair using asingle metal lock receiving recess and plurality of stitching pins withthe understanding that the pattern set forth therein is simply repeatedfor casting cracks of greater length than crack 84 shown in FIGS. 11through 14.

[0056]FIG. 12 sets forth the initial steps in completing the presentinvention casting repair method in which a plurality of stitching pins180, 181, 182 and 183 are threaded into stitching pin bores 173, 174,175 and 176 respectively. It should be understood that, in accordancewith the present invention, all stitching pins used in the presentinvention casting repair correspond in structure to stitching pin 60shown in FIG. 2. Thus, as each stitching pin is threaded into itsthreaded bore, its frustro-conical shoulder crushes the outermostthreads of the receiving bore to produce a tight seal. At the stage ofcasting repair shown in FIG. 12, stitching pins 180, 181 and 182 havebeen threaded completely into receiving bores 173, 174 and 175 and thehead portions thereof have been separated and removed through theabove-described pin shearing which occurs as each head portion separatesalong the break off groove such as groove 65 of stitching pin 60 (shownin FIG. 2). For purposes of illustration, stitching pin 183 is shownprior to the shearing of its head portion. Thereafter, the insertion ofstitching pins into the remaining threaded bores 170, 171 and 177 iscarried forward and in each insertion the head portion is removed fromthe stitching pin leaving each stitching pin firmly embedded within itsrespective threaded bore such that a portion of each stitching pinextends above the surface of casting 80. It should be noted that inaccordance with the preferred application of the present inventioncasting repair method, threaded bores 173 and 174 on either side ofrecess 150 overlap the adjacent circular lobes of recess 150 and themetal locks supported therein to provide a reliable seal on either sideof recess 150 and to further secure the metal locks inserted therein ina reliable seal.

[0057]FIG. 13 sets forth the next step of the present invention castingrepair method following the above-described insertion of stitching pinsinto threaded bores 170 through 177. This next step of the presentinvention casting repair method is shown partially completed in FIG. 13in which an additional plurality of threaded bores are drilled andtapped in overlapping interleaved spacing between the installedstitching pins. At the point of casting repair shown in FIG. 13,intermediate threaded bores 190, 191 and 192 have been drilled andtapped in an interleaved overlapping arrangement with respect tothreaded bores 174, 175, 176 and 177 and corresponding stitching pins181, 182, 183 and 187. A corresponding plurality of stitching pins 195,196 and 197 have been threaded into and received within intermediatethreaded bores 190 through 192 respectively. At the point shown in FIG.13, stitching pins 195 through 197 have been fully inserted and theheads thereof removed through the above-described break away shearingoperation. It remains in FIG. 13 to drill and tap a correspondingplurality of intermediate overlapping threaded apertures betweenstitching pins 184, 185, 186 and 180 to complete the installation ofstitching pins. Once this stitching pin installation is complete, theexcess portions of stitching pins is removed using a conventionalmaterial removal process such as grinding or the like to produce thecomplete repair shown in FIG. 14. To facilitate the full understandingof the completed repair shown in FIG. 14, the individual referencenumbers corresponding to each of the circular bores drilled during theprocess in which recess 150 was formed have been retained in FIG. 14. Itshould be recalled that each of the circular portions of lock receivingrecess 150 is formed using the same diameter drill. It should also benoted that in accordance with the present invention casting repair, theplurality of stitching pins shown in FIG. 14 completely covers crack 84in casting 80. In addition, the overlapping arrangement of stitchingpins provides for a complete and reliable seal between adjacentstitching pins in which the above-described operation of the novelstructure of stitching pin 60 (seen in FIG. 2) is utilized to its utmostadvantage.

[0058] What has been shown is an improved apparatus and method forcarrying forward a cold metal repair of a casting crack which utilizesan improved stronger and more reliable metal lock together with animproved better sealing stitching pin structure. In addition, the metallock structure used in the present invention apparatus provides amaximum of strength while maintaining a secure and tenacious grippingaction upon the casting. The present invention metal lock also providesa drawing force which is operative upon the casting to draw the castingmaterial on either side of the crack together to improve the repair sealthus provided.

[0059] While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects. Therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:
 1. A method for repairing a crack in a cast material, includingthe steps of: forming a bore in the material extending between sides ofthe crack, forming internal threads on sides of the bore, providing astitching pin having a head at one end, a tip at an opposite end, andexternal threads between the tip and the head, the external threadshaving a major diameter greater than a major diameter of the internalthreads of the bore, and threading the stitching pin into the bore. 2.The method of claim 1 including the further step of reducing a majordiameter of at least one of the threads adjacent the tip to a majordiameter less than a diameter of the internal threads.
 3. The method ofclaim 2 wherein said providing step includes the step of sizing all ofthe threads unaffected by said reducing step to have an equal diameter.4. The method of claim 3 including the further step of forming ashoulder on the stitching pin between the external threads and the head,the shoulder having a portion thereof with a diameter greater than amajor diameter of the external threads.
 5. The method of claim 4 whereinsaid forming a shoulder step includes the further steps of providing theshoulder with a greatest diameter upper portion and a least diameterlower portion, the greatest diameter upper portion having a diametergreater than the major diameter of the external threads and the leastdiameter lower portion having a diameter less than the major diameter ofthe external threads.
 6. The method of claim 5 wherein said providingstep includes the steps of: forming the tip to exhibit a conicalcontour, and forming the bore such that a bottom thereof has a bottomportion similar in size and shape to the conical contour of the tip ofthe stitching pin.
 7. The repair method of claim I including the furthersteps of: providing a lock having a major axis and a peripheral walloriented perpendicular to the major axis, the peripheral wall includinga plurality of first lobe pairs, each first lobe pair including a firstlobe on one side of the major axis and a second lobe on a secondopposite side of the major axis, the first lobe of each first lobe pairhaving a similar size and shape to the second opposite lobe of the firstlobe pair, at least one second lobe pair interposed between two adjacentfirst lobe pairs and including a first lobe having a first arcuateportion defined by a first radius of curvature and a second arcuateportion defined by a second radius of curvature, the first radius ofcurvature similar in length to the second radius of curvature, the firstradius of curvature having a first center, the second radius ofcurvature having a second center, the first center oriented closer tothe second arcuate portion than to the first arcuate portion, the secondcenter oriented closer to the first arcuate portion than to the secondarcuate portion, drilling at least one bore within the crack having aradius similar to the first radius of curvature, drilling at least twoadjacent bores at locations spaced from the crack and adjacent thecentral bore, and placing a lock into a recess formed by a combinationof the central bore and the adjacent bores.
 8. The method of claim 7wherein said providing step includes the step of forming the first lobeof each first lobe pair in a manner extending from the major axis adistance similar to a distance by which the second opposite lobe of thefirst lobe pair extends from the major axis.
 9. The method of claim 8wherein said providing step includes the step of forming each lobe ofeach adjacent first lobe pair to exhibit a circular contour defined by athird radius of curvature equal in length to the first radius ofcurvature and the second radius of curvature.
 10. The method of claim 9wherein said drilling adjacent bores step includes the step of orientingthe adjacent bores to be spaced from the central bore by a distance suchthat the adjacent bores overlap the central bore by an amount similar toan amount of overlap of the adjacent lobe pairs over at least one secondlobe pair.
 11. A repair system for repairing cracks in a casting,comprising in combination: a bore formed in the casting and penetratinga crack, said bore oriented with portions of said bore on both sides ofthe crack, said bore having sides with internal threads formed thereon,and a stitching pin, said pin being substantially cylindrical andincluding a head at one end, a tip at an opposite end and externalthreads between said head and said tip, at least one of said externalthreads having a major diameter greater than a major diameter of saidinternal threads.
 12. The system of claim 11 wherein a plurality ofexternal threads closest to said head have equal major diameters. 13.The system of claim 12 wherein at least one thread adjacent said tip hasa major diameter less than said diameter of said internal threads andall other threads have a major diameter greater than said major diameterof said internal threads.
 14. The system of claim 13 wherein said boreincludes a bottom portion at an end thereof opposite a surface of thecasting, and wherein said tip of said stitching pin includes a conicalcontour.
 15. The system of claim 14 wherein said conical contour of saidtip of said stitching pin is shaped and sized similarly to said bottomportion of said hole.
 16. The system of claim 15 wherein said stitchingpin includes a shoulder between said external threads and said head,said shoulder having a largest diameter portion larger than a majordiameter of said external threads.
 17. The system of claim 16 whereinsaid shoulder includes a least diameter portion below said greatestdiameter portion, said least diameter portion having a diameter lessthan said major diameter of said external threads and greater than aminor diameter of said external threads.
 18. The system of claim 17wherein said shoulder is frusto-conical in contour and exhibits adiameter which changes at a constant slope between said least diameterportion and said greatest diameter portion.
 19. The system of claim 18wherein said stitching pin includes a break-off groove between saidshoulder and said head, said break-off groove exhibiting a diameter lessthan a minor diameter of said external threads, whereby said stitchingpin is most susceptible to fracture at said break-off groove whentorsional loads are applied about a central axis thereof.
 20. The systemof claim 19 wherein said least diameter portion of said shoulder islocated at a junction between said shoulder and said external threads,said least diameter portion having a diameter half way between saidmajor diameter of said external threads and said minor diameter of saidexternal threads.
 21. A method for repairing a crack in a material, thesteps including: providing a lock having a major axis and including: aplurality of first lobe pairs, each first lobe pair including a firstlobe on one side of the major axis and a second lobe on a secondopposite side of the major axis, the first and second lobe being ofsimilar size and shape; and a plurality of second lobe pairs, eachsecond lobe pair including a first arcuate lobe formed on one side ofthe major axis and a second arcuate lobe formed on a second oppositeside of the major axis, such that the arcuate lobes in the secondplurality of arcuate lobe pairs radially extend outwardly beyond thelobes in the plurality of first lobe pairs, the plurality of the firstand second lobe pairs being interleaved along the major axis; forming alock receiving recess having a shape corresponding generally to the lockand extending between the sides of the crack; and inserting the lockwithin the recess wherein the lock produces a drawing force tending tomaintain the crack in tight closure and precluding crack propagation.22. The method of claim 21 wherein the forming step further includes thesteps of: forming a plurality of pilot bores on either side of thecrack; using the pilot bores for forming a plurality of substantiallyequally spaced first bores adjacent one side of the pilot bores and oneither side of the crack and forming at least one first bore in agenerally equally spaced arrangement centered along the crack; using thepilot bores for aligning the formation of a plurality of substantiallyequally spaced second bores adjacent a second opposite side of the pilotbores and on either side of the crack and forming at least one secondbore in a generally equally spaced arrangement centered along the crackwherein the plurality of the first bores and the second bores form twoprecisely positioned rows of bores in the material and with respect tothe pilot bores; and oversizing the plurality of pilot bores on eitherside of the crack wherein the pilot bores are sized to substantiallyequal the size of the first and second bores wherein the lock receivingrecess is formed at a position on each side and traversing the crack.23. The method of claim 22 further including the step of forming atleast one threaded bore in a generally equally spaced arrangementcentered along the crack.
 24. The method of claim 23 further includingthe step of providing a stitching pin having a head at one end, a tip atan opposite end and external threads interposed between the tip and thehead, the external threads having a major diameter greater than a majordiameter of internal threads of the threaded bore.
 25. The method ofclaim 24 further including the step of reducing a major diameter of atleast one of the threads adjacent the tip to a major diameter less thana diameter of the internal threads of the bore.
 26. The method of claim25 wherein said providing step includes the step of sizing all of thethreads unaffected by said reducing step to have an equal diameter. 27.The method of claim 26 further including the step of forming a shoulderon the stitching pin between the external threads and the head, theshoulder having a portion thereof with a diameter greater than a majordiameter of the external threads.
 28. The method of claim 27 wherein theforming the shoulder step further includes the step of providing theshoulder with a greatest diameter upper portion and a least diameterlower portion, the greatest diameter upper portion having a diametergreater than the major diameter of the external threads and the leastdiameter lower portion having a diameter less than the major diameter ofthe external threads.
 29. The method of claim 28 further including thestep of interposing a frangible groove between the head and the shoulderof the stitching pin, wherein said frangible groove exhibits a diameterless than the minor diameter of the external threads whereby thestitching pin is most susceptible to fracture at said frangible groovewhen torsional loads are generally applied about a central axis of thestitching pin.
 30. The method of claim 29 further including the steps offorming the tip of the stitching pin to exhibit a conical contour; andforming the threaded bore such that the bottom thereof has a bottomportion similar in size and shape to the conical contour of the tip ofthe stitching pin.
 31. The method of claim 30 further including the stepof disposing the stitching pin into the threaded bore and applying atorsional load to the head of the threaded bore, thereby threading thestitching pin into the threaded bore until the stitching pin fracturesat the frangible groove.
 32. The method of claim 31 further includingthe step of removing excess portions of the stitching pin wherein thestitching pin is substantially flush with a surface of the material.